Our long term objectives are to gain further understanding of the neural processes that enable us to move our limbs rapidly and accurately to targets around us and to explain the disordered accuracy of patients with sensory impairment and cerebellar dysmetria. We also hope to devise effective methods for improving motor performance in such patients. Our approach is to analyze in detail the performance of a simple motor task to uncover fundamental principles by which the nervous system controls the musculoskeletal system. The present proposal extends work accomplished in the current period that was focused exclusively on the production of simple isometric responses. First, we plan to determine how the amplitude and direction of an aimed response are specified using information derived from a target. The problem is addressed using a new experimental procedure by which the time interval from stimulus to response can be varied systematically. Second, we plan to determine the differences in control strategies used for the producing force and position trajectories when subjects are faced with different loading conditions. Particular attention is given to the problem of decelerating inertial loads using accurately timed commands to antagonists. Third, we plan to analyze the disorders in trajectory formation of patients with severe sensory neuropathies. Preliminary observations in two patients indicate that inaccurate performance results from impairment in the ability to program trajectory parameters as well as from an inability to make effective use of internal feedback mechanisms to correct initial trajectory errors. Proposed experiments will use auditory cues to substitute for the lost proprioceptive information in order to improve accuracy and updating. Fourth, we will initiate a study of cerebellar dysmetria to determine the mechanisms responsible for the inaccuracy and the delays in movement initiation shown by such patients.